This invention relates to compositions and methods for disruption of insect behaviors mediated by sex pheromones.
A number of attempts are being made to find new biorational and environmentally safe methods for insect pest control. Particular interest has been focused in the field of insect pheromones and other semiochemicals (i.e., chemicals which function as a signal to the organism).
An adult male moth is able to locate a pheromone-emitting female or synthetic pheromone source by a program of in-flight upwind steering (optomotor anemotaxis) and a program of counterturning. Both programs are switched on by the correct species-specific pheromone blend, and thus successful orientation and mating depends on initial olfactory events that occur at the antennal level. The crucial events involved in pheromone olfaction include adsorption of the airborne pheromone onto the antennal surface, followed by diffusion to a receptor site with subsequent binding and activation of the receptor, either by directly opening ion channels in the membrane or by activating a second messenger in order to cause a change in membrane conductance.
Recent evidence indicates that the intermittency of the pheromone signal in a natural plume that has a fine, filamentous structure is required in order for the insect to exhibit the sustained upwind flight that is necessary for location of the pheromone source. Further evidence at the single antennal neuron level indicates that the inability of the antenna to rapidly inactivate the pheromone molecules before the next filament arrives (usually in one second or less) contributes to adaptation of the neurons, which is also correlated with the cessation of sustained upwind flight.
Inactivation is believed to involve, among other things, the chemical alteration of the pheromone to an inactive form. In those cases where the pheromone is a carboxylic ester, chemical alteration is achieved by rapid hydrolytic degradation mediated by a carboxylesterase to the inactive alcohol and acid [Ferkovich et al., J. Chem. Ecol. 8:859-66 (1982)].
Among the approaches to the understanding of the molecular mechanism of pheromones activating the transductory process in insect neurons currently being investigated are (i) the use of radioligands to characterize the pheromone binding sites, and (ii) synthesis and determination of relative activities of pheromone analogs. With respect to the latter approach, the analogs Z9-14:Nmc [A], Z9-14:Tfa [B], Z9-14:Tca [C] and (Z)-12-heptadecen-2-one [D] have been reported to show reversible inhibition of electrophysiological and behavioral responses in Heliothis virescens [Baker et al., European Patent Appln. 42228 (1981); Albans et al., Crop Prot. 3:501-06 (1984)]. ##STR2##
Recently, mono , di- and tri-halogenated acetates [E], diazoacetate [F] and trifluoromethyl ketone [G] analogs of Z11-16:Ac, pheromone of Plutella xylostella, were studied as competitive inhibitors of antennal esterases [Prestwich and Streinz, J. Chem. Ecol. 14: 1003-21 (1988)]. The fluoro compounds showed greater inhibition of esterases, but were electrophysiologically less active than the natural pheromone. The compounds were not investigated further. No disruption of behavioral orientation to the natural pheromone blend was demonstrated for these compounds. ##STR3##
It is an object of the present invention to provide novel compositions which interfere with the orientation and mating of a wide range of insect species.
It is a particular object of the present invention to provide compositions and methods useful to disrupt insect mating by selective inhibition of the antennal carboxylesterase enzyme.
It is a further object of the present invention to provide such compositions and methods which have a high species specificity and reduced toxicity to other organisms relative to other insecticides heretofore in general use.